The invention concerns a tiltable arc furnace in which a furnace vessel and a portal for an electrode lifting and pivoting apparatus are arranged on a platform of a furnace cradle which is tiltable by means of a tilting apparatus and which includes three mutually spaced parallel cradle runner skids which each run on a respective support path, wherein the furnace vessel is arranged on a first platform portion (vessel platform portion) which is between two cradle runner skids and the portal is arranged on a separate second platform portion (portal platform portion) which is outside said cradle runner skids and which is tiltable by the tilting apparatus synchronously with the vessel platform portion carrying the furnace vessel.
Of the various designs for arc furnaces, in modern furnaces the variant having a common furnace support stage or furnace platform for furnace vessel and portal has gained extensive acceptance. The furnace platform therefore also carries the portal with the electrode guide columns, the cover lifting mechanism and the associated pivoting and drive mechanisms. The entire furnace is tiltable by means of a tilting apparatus, for example cylinders, by way of a cradle. When that happens, the cradle runner skids are guided on a support path. The furnace usually has two runner skids and thus two support paths which are disposed parallel to the direction of tilting movement on stable foundations. The geometry of the cradle and the support path determines the tilting motion of the furnace vessel. The main support path which is between the vessel and the portal has to carry between about 60% and 700% of the total vertical load, because of the overhanging portal portion.
FR-855 303 A discloses a tiltable arc furnace in which the overhanging part of the platform which carries the portal is supported at the outside by a third cradle sector so that the continuous cradle platform is supported on three parallel cradle sectors. That results in a statistically indefinite application of load.
Special machines are required to machine the bearing seat for the portal for that machining operation can only be effected after the welding procedure, because of the possibility of distortion.
During operation of the furnace distortion can occur because of the different effects of heat acting on the arrangement and stresses within the platform. That for example has an adverse influence on the correctness of the electrode travel paths and the regulation thereof. Correction of the distortion is not possible without expensive and time-consuming dismantling of the vessel, portal and platform.
In the modernization of existing furnaces, it becomes necessary to install a fresh portal for better and faster electrode regulation. Aligning and adapting the platform is then very complicated and expensive.
German published specification (DE-AS) No 11 08 830 discloses a tiltable arc furnace in which the electrode portal is arranged on a cradle which is separate from the furnace cradle and which can either be coupled to the furnace cradle by a first boltxe2x80x94that is intended for the small tilting movements in the slag tapping operationxe2x80x94or which can be fixed to a stationary mounting by means of a second bolt. The last-mentioned possibility is provided in order to ensure that, when implementing major tilting movements of the furnace vessel, in the tapping operation, the electrodes do not also have to be tilted, which results in electrode fractures. For the tapping operation therefore the electrodes are previously drawn from the vessel and the separate cradle is fixed to the stationary mounting by means of the second bolt.
In accordance with the invention a tiltable arc furnace of the kind set forth in the opening part of this specification is designed in such a way that the two platform portions are connected together by at least one hinge pivot whose axis of rotation extends parallel to the intersection line between a platform plane and the plane in which a cradle runner skid lies.
The structure according to the invention can be implemented in existing furnaces if for example the portal has to be renewed. The stoppage times can then be substantially reduced. It is also possible without any problem firstly to convert the platform with the portal and then, at a later moment in time, to convert the platform with the furnace vessel. If the configuration according to the invention is embodied in a fresh installation, the subsequent replacement of portal and/or vessel is substantially easier.
An additional tilting apparatus can be mounted to the portal platform, the additional tilting apparatus operating synchronously with the main tilting apparatus.